Food prepared at home is slowly getting healthier, but food prepared away from home is not, according to a new study by the USDA Economic Research Service.

Food prepared away from home accounts for 32 percent of Americans’ caloric intake and 41 percent of food expenditures. (Food prepared away from home includes restaurants, fast-food establishments, and take-out or delivery meals.)

Americans increased their away-from-home share of calories from 18 percent to 32 percent in the last three decades, mainly from table-service and fast-food restaurants.

Caloric intake rose over the last three decades from 1,875 calories per person per day to 2,002 calories per day.

Food prepared at home became significantly lower in fat content and richer in calcium over the past three decades; food prepared away from home did not.

Food prepared away from home is higher in saturated fat, sodium, and cholesterol, and lower in dietary fiber than food prepared at home.

Poor diets contribute to obesity, heart disease, cancer, diabetes, and other health conditions. The trend toward eating out is expected to continue, so Americans need to learn how their food is prepared, and what’s in it. Only then will they have the information to make wise food choices.

Consumers should be health-savvy when they eat away from home. Don’t be afraid to ask for nutritional information or preparation methods, and don’t assume that restaurants (even high-end restaurants) serve healthy food. Restaurants serve what consumers like — fat, salt, sugar and lots of calories. The American Heart Association offers a variety of very useful information for dining out, and the Center for Science in the Public Interest has guidelines on labeling at fast-food and chain restaurants.

Some fast-food restaurants have pamphlets available with nutritional information — it’s surprising to find how high in calories and fat some menu items are. Beware, though, of what they consider a serving size — it may be less than what is purchased as a single serving. A report in the Los Angeles Times notes that few entrees at fast-food restaurants meet the USDA-recommended limits for calories, sodium, saturated fat and fat combined.

Opt for healthier choices, and don’t feel compelled to “clean your plate” at meals. Some people routinely eat no more than half the restaurant meal, saving the other half for another meal. Ask your restaurants to serve healthier options — restaurants will respond only if consumers commit to making healthy food choices.

There is hope. Americans may be getting the message about dietary fat — consumption of fat has dropped from 86 grams of total fat per person per day to 75 grams per day over the last three decades. But, on average, food prepared away from home still has more fat (37 percent) than food prepared at home (30 percent).

Due to the increase in consumption of food prepared away from home, we may see more of a push to include nutritional and health information on menus (see the proposed FDA guidelines). Whether this impacts consumer food choices remains to be seen. But by learning some basics about food and nutrition, you can make healthier choices, even when eating at restaurants.

The University of California offers many free and low-cost publications on food, health and nutrition. Here are a few: